1. Field of the Invention
The present invention relates to a rotor structure of an electric rotating machine such as ac generator or electric motor and, more particularly, to a structure of fitting a magnet that prevents leakage of magnetic flux between claw magnetic poles.
2. Description of the Related Art
In a conventional rotor structure, rectangular parallelepiped magnets polarized in a direction of reducing leakage of magnetic flux between sides of adjacent claw magnetic poles are fixed between the claw magnetic poles facing each other, and holders for reducing centrifugal force are used to fit these magnets.
When the magnets for preventing leakage of magnetic flux are fitted to the claw magnetic poles of a rotor core as described above, the claw magnetic poles increase in weight. Therefore, end of each claw magnetic pole reciprocates toward a rotor coil and a stator due to centrifugal force caused by rotation of the rotor and magnetic attraction between the claw magnetic pole and the stator produced at the time of power generation.
As a result, a load is applied to the magnets between the claw poles, and this sometimes may cause distortion or breakage of the magnets.
To overcome this, in a conventional rotor, a magnet is fixed to each claw magnetic pole in such a manner as to cover an inner circumferential face and a side face of the claw magnetic pole.
In this known construction, spaces are left between the adjacent magnets.
As a result, the claw magnetic poles and the magnets reciprocate independently, therefore any load is not applied to the magnets, and it is possible to prevent the magnets from breakage (for example, see the Japanese Patent Publication (unexamined) No. 1999/136913, pages 3 and 4).
In another conventional rotor, each claw magnetic pole is provided with two ferrite magnets on both side faces of each claw pole, and these magnets are polarized so as to reduce leakage of magnetic flux between the claw magnetic poles.
These magnets are supported on the claw magnetic poles, with a slant so as to spread their outer circumference sides toward each other, by magnet-holding members for absorbing centrifugal force that acts on the mentioned magnets when the rotor is rotating through deformation of the magnet-holding members themselves. Thus, the magnets are so constructed as to withstand centrifugal force (for example, see the Japanese Patent Publication (unexamined) No. 2001/86715, page 6).
The permanent magnets are fitted to the claw magnetic poles for the purpose of reducing leakage of magnetic flux between the side faces of the adjacent claw magnetic poles and leakage of magnetic flux from their inside diameter faces, thereby improving output of the electric rotating machine.
However, fitting the magnets brings about a contrary effect, i.e., the claw magnetic pole as a whole increases in weight and the claw magnetic pole receives more centrifugal force caused by rotation of the rotor.
In particular, increase in weight of the end portion of the claw magnetic pole invites increase in deformation spreading toward a stator.
Hence, it is necessary to enlarge an air gap between the rotor and the stator in order to prevent breakage.
However, this air gap has a close relationship to the output, i.e., the more the air gap is decreased, the more output is increased.
Therefore, it is necessary that the magnets be fixed so as to restrain deformation of the claw magnetic poles from the viewpoint of further improving the output.
In the meanwhile, the magnet-holding members for fitting the magnets to the claw magnetic poles are influenced by the deformation of the claw magnetic poles and change in number of rotation of the rotor, and there is a possibility that the magnet-holding members or the magnets themselves are broken or get out of position due to vibration of the claw magnetic poles.
Moreover, the known structure of fitting the magnets to the claw magnetic poles also has a problem that it is not possible to efficiently assemble the rotor because interference in magnetic position occurs between the pole cores at the time of assembling rotor.